1. Field of the Invention
This invention relates to an information-signal encrypting apparatus and an information-signal decrypting apparatus. This invention also relates to a group of designated machines each provided with at least one of an information-signal encrypting apparatus and an information-signal decrypting apparatus which are designed to permit important contents information such as copyrighted contents information to be copied and reproduced by the designated machines, and to prevent the important contents information from being copied and reproduced by machines other than the designated ones.
2. Description of the Related Art
It is known to encrypt copyrighted contents information and then record the encryption-resultant information on a recording medium. A duplicate of the recording medium also stores the encryption-resultant information. The encryption-resultant information can be read out from the duplicate. A third party that does not know a key for decrypting the encryption-resultant information can not recover the original copyrighted contents information from the read-out encryption-resultant information. Therefore, it is possible to prevent the copyrighted contents information from being illegally copied.
Japanese patent application publication number 2002-169740 discloses a system including a contents server, an information reproducing terminal, and an IC card. In the system of Japanese patent application 2002-169740, electronic data representing encrypted contents is transmitted or downloaded from the contents server to the terminal via a network and an access point before being written into a memory within the terminal. When the IC card is inserted into the terminal, the contents server and the IC card can communicate with each other via the network, the access point, and the terminal. During the communication, a key for the encrypted contents is sent from the contents server to the IC card before being written into a memory within the IC card. The terminal can be operated in a reproducing mode. When the terminal is operated in the reproducing mode, the IC card is inserted in the terminal. During the reproducing mode of operation of the terminal, the key for the encrypted contents is fed from the IC card to the terminal, and the terminal decrypts the electronic data in response to the key to recover the original contents.
In the system of Japanese patent application 2002-169740, a certification key (an authentication key) is prestored in a memory within the IC card. Before the download of the electronic data from the contents server to the terminal is started, the server and the IC card communicate to confirm whether a user is legitimate on the basis of the certification key. After it is confirmed that the user is legitimate, the download of the electronic data from the contents server to the terminal is started. In addition, the transmission of the key for the encrypted contents from the contents server to the IC card is implemented. There is a possibility that the key for the encrypted contents will be eavesdropped on during the transmission thereof.
Typical DVD (digital versatile disc) recorder/players called typical DVD machines have functions of encrypting contents information and then recording the encryption-resultant information on DVD's. The DVD recorder/players also have functions of reading out encryption-resultant information from DVD's and then decrypting the read-out information to recover original contents information. The DVD recorder/players are compatible with each other in recording and reproducing features. In addition, the DVD recorder/players have common encrypting and decrypting functions. Therefore, one DVD machine can reproduce contents information from encryption-resultant information generated by another DVD machine. Thus, in the case where two different homes have DVD machines respectively, it is difficult to limit an area, in which the copying of contents information is permitted, to only one of the two homes.
Similarly, D-VHS recorder/players (D-VHS machines) have functions of encrypting contents information and then recording the encryption-resultant information on magnetic tapes. The D-VHS recorder/players also have functions of reading out encryption-resultant information from magnetic tapes and then decrypting the read-out information to recover original contents information. The D-VHS recorder/players are compatible with each other in recording and reproducing features. In addition, the D-VHS recorder/players have common encrypting and decrypting functions. Therefore, one D-VHS machine can reproduce contents information from encryption-resultant information generated by another D-VHS machine. Thus, in the case where two different homes have D-VHS machines respectively, it is difficult to limit an area, in which the copying of contents information is permitted, to only one of the two homes.
In general, the encryption of contents information uses an encryption key. In this case, the contents information can be recovered from the encryption-resultant information by referring to the encryption key.
In the case where both encryption-resultant information and an encryption key which has been used to encrypt contents information into the encryption-resultant information are recorded on a single recording medium, a third party can easily obtain both the encryption-resultant information and the encryption key by accessing the recording medium. Thus, the third party can easily reproduce the contents information from the encryption-resultant information by referring to the encryption key. To remove such a problem, the contents information is further subjected to encryption for an interface.